Gaia philosophy (named after Gaia, Greekgoddess of the Earth) is a broadly inclusive term for related concepts that living organisms on a planet will affect the nature of their environment in order to make the environment more suitable for life. This set of theories holds that all organisms on a life-giving planet regulate the biosphere in such a way as to promote its habitability. Gaia concept draws a connection between the survivability of a species (hence its evolutionary course) and its usefulness to the survival of other species.

While there were a number of precursors to Gaia theory, the first scientific form of this idea was proposed as the Gaia hypothesis by James Lovelock, a UK chemist, in 1970. The Gaia hypothesis deals with the concept of Biological homeostasis, and claims the resident life forms of a host planet coupled with their environment have acted and act like a single, self-regulating system. This system includes the near-surface rocks, the soil, and the atmosphere. Today many scientists consider such ideas to be unsupported by, or at odds with, the available evidence (see recent criticism). These theories are however significant in green politics.

There are some mystical, scientific and religious predecessors to the Gaia philosophy, which had a Gaia-like conceptual basis. Many religious mythologies had a view of Earth as being a whole that is greater than the sum of its parts (e.g. some Native American religions and various forms of shamanism).

Lewis Thomas believed that Earth should be viewed as a single cell; he derived this view from Johannes Kepler's view of Earth as a single round organism.

Isaac Newton wrote of the earth, "“Thus this Earth resembles a great animall or rather inanimate vegetable, draws in æthereall breath for its dayly refreshment & vitall ferment & transpires again with gross exhalations, And according to the condition of all other things living ought to have its times of beginning youth old age & perishing.”[1]

Pierre Teilhard de Chardin, a paleontologist and geologist, believed that evolution unfolded from cell to organism to planet to solar system and ultimately the whole universe, as we humans see it from our limited perspective. Teilhard later influenced Thomas Berry and many Catholic humanist thinkers of the 20th century.

Buckminster Fuller is generally credited with making the idea respectable in Western scientific circles in the 20th century. Building to some degree on his observations and artifacts, e.g. the Dymaxion map of the Earth he created, others began to ask if there was a way to make the Gaia theory scientifically sound.

None of these ideas are considered scientific hypotheses; by definition a scientific hypothesis must make testable predictions. As the above claims are not testable, they are outside the bounds of current science.

These are conjectures and perhaps can only be considered as social and maybe political philosophy; they may have implications for theology, or thealogy as Zell-Ravenheart and Isaac Bonewits put it.

According to James Kirchner there is a spectrum of Gaia hypotheses, ranging from the undeniable to radical. At one end is the undeniable statement that the organisms on the Earth have radically altered its composition. A stronger position is that the Earth's biosphere effectively acts as if it is a self-organizing system which works in such a way as to keep its systems in some kind of equilibrium that is conducive to life. Today many scientists consider that such a view (and any stronger views) are unlikely to be correct.[3][4][5][6][7] An even stronger claim is that all lifeforms are part of a single planetary being, called Gaia. In this view, the atmosphere, the seas, the terrestrial crust would be the result of interventions carried out by Gaia, through the coevolving diversity of living organisms.

The most extreme form of Gaia theory is that the entire Earth is a single unified organism with a highly intelligent mind that arose as an emergent property of the whole biosphere. In this view, the Earth's biosphere is consciously manipulating the climate in order to make conditions more conducive to life. Scientists contend that there is no evidence at all to support this last point of view, and it has come about because many people do not understand the concept of homeostasis. Many non-scientists instinctively and incorrectly see homeostasis as a process that requires conscious control[dubious– discuss][citation needed].

The more speculative versions of Gaia, including versions in which it is believed that the Earth is actually conscious, sentient, and highly intelligent, are usually considered outside the bounds of what is usually considered science.

A variant of this hypothesis was developed by Lynn Margulis, a microbiologist, in 1979. Her version is sometimes called the "Gaia Theory" (note uppercase-T). Her model is more limited in scope than the one that Lovelock proposed.

Whether this sort of system is present on Earth is still open to debate. Some relatively simple homeostatic mechanisms are generally accepted. For example, when atmosphericcarbon dioxide levels rise, plants are able to grow better and thus remove more carbon dioxide from the atmosphere. Other biological effects and feedbacks exist,[7] but the extent to which these mechanisms have stabilized and modified the Earth's overall climate is largely not known.

The Gaia hypothesis is sometimes viewed from significantly different philosophical perspectives. Some environmentalists view it as an almost conscious process, in which the Earth's ecosystem is literally viewed as a single unified organism. Some evolutionary biologists, on the other hand, view it as an undirected emergent property of the ecosystem: as each individual species pursues its own self-interest, their combined actions tend to have counterbalancing effects on environmental change. Proponents of this view sometimes point to examples of life's actions in the past that have resulted in dramatic change rather than stable equilibrium, such as the conversion of the Earth's atmosphere from a reducing environment to an oxygen-rich one.

Depending on how strongly the case is stated, the hypothesis conflicts with mainstream neo-Darwinism. Most biologists would accept Daisyworld-style homeostasis as possible, but would certainly not accept the idea that this equates to the whole biosphere acting as one organism.

A very small number of scientists, and a much larger number of environmental activists, claim that Earth's biosphere is consciously manipulating the climate in order to make conditions more conducive to life. Scientists contend that there is no evidence to support this belief.

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A social science view of Gaia theory is the role of humans as a keystone species who may be able to accomplish global homeostasis. Whilst a few social scientists who draw inspiration from 'organic' views of society have embraced Gaia philosophy as a way to explain the human-nature interconnections, most professional social scientists are more involved in reflecting upon the way Gaia philosophy is used and engaged with within sub-sections of society. Alan Marshall, in the Department of Social Sciences at Mahidol University, for example, reflects upon the way Gaia philosophy has been used and advocated by environmentalists, spiritualists, managers, economists, and scientists and engineers (see The Unity of Nature, 2002, Imperial College Press: London and Singapore). Social Scientists themselves in the 1960s gave up on systems ideas of society since they were interpreted as supporting conservatism and traditionalism.

Some radical political environmentalists who accept some form of the Gaia theory call themselves Gaians. They actively seek to restore the Earth's homeostasis — whenever they see it out of balance, e.g. to prevent manmade climate change, primate extinction, or rainforest loss. In effect, they seek to cooperate to become the "system consciously manipulating to make conditions more conducive to life". Such activity defines the homeostasis, but for leverage it relies on deep investigation of the homeorhetic balances, if only to find places to intervene in a system which is changing in undesirable ways.

Tony Bondhus brings up the point in his book, Society of Conceivia, that if Gaia is alive, then societies are living things as well. This suggests that our understanding of Gaia can be used to create a better society and to design a better political system.

Other intellectuals in the environmental movement, like Edward Goldsmith, have used Gaia in the completely opposite way; to stake a claim about how Gaia's focus on natural balance and resistance and resilience, should be emulated to design a conservative political system (as explored in Alan Marshall's 2002 book The Unity of Nature, (Imperial College Press: London).

Gaians argue that it is a human duty to act as such - committing themselves in particular to the Precautionary Principle. Such views began to influence the Green Parties, Greenpeace, and a few more radical wings of the environmental movement such as the Gaia Liberation Front and the Earth Liberation Front. These views dominate some such groups, e.g. the Bioneers. Some refer to this political activity as a separate and radical branch of the ecology movement, one that takes the axioms of the science of ecology in general, and Gaia theory in particular, and raises them to a kind of theory of personal conduct or moral code.

Many new age authors have written books which mix New Age teachings with Gaia philosophy. This is known as New Age Gaian. Often referred to as Gaianism, or the Gaian Religion, this spiritual aspect of the philosophy is very broad and inclusive, making it adaptable to other religions: Taoism, Neo-Paganism, Pantheism, Judeo-Christian Religions, and many others.

The question of "what is an organism", and at what scale is it rational to speak about organisms vs. biospheres, gives rise to a semantic debate. We are all ecologies in the sense that our (human) bodies contain gut bacteria, parasite species, etc., and to them our body is not organism but rather more of a microclimate or biome. Applying that thinking to whole planets:

The argument is that these symbiotic organisms, being unable to survive apart from each other and their climate and local conditions, form an organism in their own right, under a wider conception of the term organism than is conventionally used. It is a matter for often heated debate whether this is a valid usage of the term, but ultimately it appears to be a semantic dispute. In this sense of the word organism, it is argued under the theory that the entire biomass of the Earth is a single organism (as Johannes Kepler thought).

Unfortunately, many supporters of the various Gaia theories do not state exactly where they sit on this spectrum; this makes discussion and criticism difficult.

Much effort on behalf of those analyzing the theory currently is an attempt to clarify what these different hypotheses are, and whether they are proposals to 'test' or 'manipulate' outcomes. Both Lovelock's and Margulis's understanding of Gaia are considered scientific hypotheses, and like all scientific theories are constantly put to the test.

More speculative versions of Gaia, including all versions in which it is held that the Earth is actually conscious, are currently held to be outside the bounds of science, and are not supported by either Lovelock or Margulis.

One of the most problematic issues with referring to Gaia as an organism is its apparent failure to meet the biological criterion of being able to reproduce. Richard Dawkins has asserted that the planet is not the offspring of any parents and is unable to reproduce.[10]

Isaac Asimov in his 1982 novel Foundation's Edge describes a planet known as Gaia, which is a 'superorganism'. All things on Gaia participate in a larger, group consciousness, while still retaining any individual awareness they might have, such as among the Gaian humans. Gaians were important in shaping the future course of Asimov's universe.

At least one work of fiction, the film Final Fantasy: The Spirits Within, uses Gaia philosophy as a central point to the plot, and may arguably represent a fictional parallel to Sir James Lovelock in the character of Dr. Cid, who is met with skepticism from the scientific and social community when he promotes the idea of a "living Earth". In the film, Dr. Cid attempts to create a "waveform" from the positive energy signature of the Earth's spirit, in order to combat the films antagonists, the negative energy "Phantoms", through use of phase inversion canceling.

In addition, Gaia philosophy is prominent in the video game Final Fantasy VII, where the theme of a living planet in which all life is one is symbolized by the idea of the Lifestream. The Lifestream is not only a philosophical theme present in the game, but it actually acts as a plot device, "erupting" at certain points in the game. In the context of Final Fantasy VII and its various spin-offs (which include three games and a movie), the Lifestream is a collection of all the souls and energy on the earth, and is semi-sentient. In fact, in Dirge of The Cerberus, a spin-off game, it is revealed that the Lifestream can and will transplant itself from a planet when that place becomes too dangerous.

Computer game Sid Meier's Alpha Centauri and its expansion Sid Meier's Alien Crossfire are set on the planet Chiron in the Alpha Centauri system where all indigenous life appears to behave in accordance with the Gaia philosophy. The intelligent force behind this behavior is called simply "Planet" and, in the expansion, is revealed to be artificially created by an alien race. At the time the game takes place, Planet is nearing its self-awareness threshold. Normally, the nature of Planet's life causes it never to attain full sentience; however, human presence adds an unknown variable into the equation.

The Gaia philosophy is a guiding principle for terrorists in the Tom Clancy novel Rainbow Six.

The film Avatar depicts a world (Pandora) that functions like a single organism, in which various species of earth and sky cooperate with the humanoid population (the Na'vi) to defend the planet against a corporate-military invasion.